Ester formation of fatty acid and hydroxycarboxylic acid

ABSTRACT

The present invention relates to a process for the transesterification of a fatty acid ester of a lower alcohol and a salt hydroxycarboxylic acid without making use of organic solvents. The process can also be carried out without added anionic surface active agents.

The present invention relates to a process for the preparation of a saltof a fatty acid ester of hydroxycarboxylic acid, in particular a salt ofa fatty acid ester of lactic acid which is also called a lactylate.

Salts of fatty acid esters of hydroxycarboxylic acids are known to beuseful as emulsifier in food applications, as emulsifier in cosmeticapplications for home and personal care and as growth promoter in AnimalHealth.

Such a compound can be prepared by direct esterification of lactic acidand a fatty acid as has been described in U.S. Pat. No. 2,733,252. Animproved process has been described in U.S. Pat. 5,872,268, wherein afatty acid ester of a lower alcohol and a salt of hydrocarboxylic acidare subjected to ester interchange. This process, however, requires thepresence of an organic solvent and a nonionic or anionic surface activeagent.

According to the present invention a process has been found which makesuse of an ester interchange between a fatty acid ester of a loweralcohol and a salt of hydrocarboxylic acid without making use of organicsolvents. Also added anionic surface active agents are not necessary.

The process has the advantage that there is a high conversion into thesalt of the required fatty acid ester of hydroxycarboxylic acidresulting in a high amount of the desired ester.

The reaction also selectively moves towards the fatty acid ester of amonomeric hydroxycarboxylic acid (e.g. 1-lactylate or monolactylate) andin the resulting end product no azeotropic mixture with free fatty acidsis formed.

Furthermore, the process is more convenient in that there is lessblocking of accumulating fatty acids in the equipment.

The present invention pertains to a process for the preparation of asalt of a fatty acid ester of hydroxycarboxylic acid which comprisesheating a salt of hydroxycarboxylic acid with a catalyst in admixturewith a C8-C24 fatty acid (i.e. having 8 to 24 carbon atoms) ester of alower alcohol having 1-4 carbon atoms at a temperature at which thereexists a liquid phase and subjecting the mixture to ester interchangewhereby the temperature of the process is kept at or below the boilingpoint of the C8-C24 fatty acid ester of a lower alcohol having 1-4carbon atoms.

This process solves the disadvantages mentioned here above for thehitherto known processes. The process does not require the use orpresence of an organic solvent in an amount necessary to form a liquidstate as the salt of the hydroxycarboxylic acid in admixture with thefatty acid ester is in its liquid state. The process also does not needthe use of a nonionic or anionic surface active agent in an amountnecessary to enhance or cause mixing because spontaneous mixing of thereactants occurs during the reaction.

Hereinafter, the present invention is further described in detail.

The type of hydroxycarboxylic acid salt used according to the presentinvention can be any type of hydroxycarboxylic acid salt inasfar as itcan form a liquid mixture or dispersion with the fatty acid ester of alower alcohol. Thereto, hydrocarboxylic acid as used herein means a monoor di carboxylic acid molecule having 2-4 carbon atoms and 1-3 hydroxylgroups. Examples are lactic acid, malic acid and tartaric acid. With theterm hydroxycarboxylic acid salt is, in addition to the regular salts ofhydroxycarboxylic acid, also meant a cyclic carboxylic acid. Preferredare metal salts, in particular alkaline metal salts or alkaline earthmetal salts. The preferred hydroxycarboxylic acid is lactic acid. Mostpreferred are sodium or potassium lactate or magnesium or zinc lactate.Even more preferred are sodium or potassium lactate. The preferredcyclic hydroxycarboxylic acid is lactide.

The type of alkyl ester constituting the fatty acid moiety of the fattyacid ester of lower alcohol according to the present inventionpreferably has a boiling point above the melting point of thehydroxycarboxylic acid salt, to keep the whole process liquid. The alkylester molecule contains two alkyl groups: the ‘acid’ part can be anylength, as long as it is liquid at the desired reaction temperature. The‘alcohol’ part needs to be sufficiently short, to be able to evaporateupon reaction.

Examples of fatty acids include saturated or unsaturated fatty acidswith 8-24 carbon atoms. Also branched chain fatty acids or one or morehydroxyl groups may be used. Examples of such fatty acids are caprylicacid, capric acid, lauric acid, myristic acid, palmitic acid stearicacid, oleic acid linoleic acid, alpha linolenic acid, ricinolleic acid,petroselinic acid, arachidic acid and behenic acid. Preferred fattyacids are fatty acids with 8-18 carbon atoms (C8-C18). More preferredare fatty acids with 12-18 carbon atoms (C12-C18), more preferred with12-14 carbon atoms (C12-C14). Most preferred is a fatty acid with 12carbon atoms.

As the lower alcohol moiety of the fatty acid ester of lower alcohol inthe present invention, a primary alcohol having 1-4 carbon atoms (suchas methanol, ethanol, propanol or butanol) or a mixture thereof may beused. These alcohols can easily be removed in the course of thetransesterification reaction by vaporization. Preferred alcohols aremethanol and ethanol or a mixture thereof.

Preferred fatty acid ester of a lower alcohol is methyl laurate.Preferred hydroxycarboxylic acid salt is sodium lactate. The reactionprocess can also be carried out with mixtures of different C8-C24 fattyacid esters of the lower alcohol having 1-4 carbon atoms. Preferred aremixtures with fatty acids with 12, 14, 16 and/or 18 carbon atoms. Thelower alcohol preferably has 1-2 carbon atoms, most preferably ismethanol.

In one embodiment the salt of the hydroxycarboxylic acid is first heatedwith the catalyst to a temperature equal to or above the meltingtemperature of the hydroxycarboxilic acid salt and then the C8-C24 fattyacid ester of the lower alcohol is added. Thereafter the mixture issubjected to the transesterification reaction at a temperature asindicated above i.e. at or between the melting point of thehydroxycarboxylic acid salt and the boiling point of the C8-C24 fattyacid ester of a lower alcohol having 1-4 carbon atoms. Alternatively,the catalyst can also be added in a later stage e.g. with the additionof the C8-C24 fatty acid ester.

The temperature of the reaction is chosen such that the mixture of thetwo reagents i.e. the salt of hydroxycarboxylic acid and the C8-C24fatty acid ester of a the lower alcohol having 1-4 carbon atoms are inthe liquid stage. With the term liquid stage or liquid phase it is meantthat the mixture is a real liquid, or is a dispersion, suspension,emulsion, colloid or the like.

As mentioned here above the process does not require the presence of anorganic solvent. Added nonionic or anionic surface active agent can bepresent, but may also be absent.

In one embodiment less than 15 mol % based on the salt of thehydroxycarboxylic acid may be present. In another embodiment less than10 mol % of surfactant is present. In yet another embodiment less than 5mol % of surfactant is present. In another embodiment no added nonionicor anionic surface active agents are present.

The preferred temperature range of the transesterification reaction isbetween the melting temperature of the salt of the hydroxycarboxylicacid and the boiling point of the C8-C24 fatty acid ester of a loweralcohol having 1-4 carbon atoms.

Almost any sufficiently strong alkali catalyst can be used in thepresent reaction. The catalyst should be able to deprotonate the alcoholgroup of the hydroxycarboxylic acid.

Preferably, the catalyst used in the present reaction has the generalformula alkali-OR wherein R stands for H or (C1-C3)alkyl. Preferably,the alkyl group is methyl. The metal moiety of the alkali catalyst ispreferably the same as the metal moiety of the salt of hydroxycarboxylicacid in the reaction. Preferably this is sodium. The amount of catalystto be added is from 0.01 to 20 mol % based on the fatty acid ester oflower alcohol. In case lactide is used as hydroxycarboxylic acid sourcea higher amount of alkali might be added to convert the lactide tolactate.

The content of salt of hydroxycarboxylic acid is from 0.2 to 20,preferably from 0.5-3 mols per mol of the fatty acid ester of a loweralcohol having 1-4 carbon atoms.

In a typical reaction, the salt of hydroxycarboxylic acid is mixed withthe catalyst and heated to a temperature such that the mixture willmelt. Preferably the temperature is in the range of 160-200° C. Sodiumlactate has a melting point of 161-162° C. Thus, if sodium lactate isused as the source of the hydroxycarboxylic acid salt the temperatureshould be preferably above this melting point range. Water or alkanol(e.g. methanol) arising through the reaction will be removed from thereaction mixture by vaporization, creating vacuum or by distillation.Then the C8-C24 fatty acid ester of a lower alcohol having 1-4 carbonatoms is added slowly. A one phase, milky type of reaction mixture willbe formed quickly. The reaction will be continued at the hightemperature and methanol will be removed by creating a vacuum orbubbling through an inert gas. The reaction can be monitored e.g. by TLCand/or GC. If the reaction is completed, the reaction can be stopped bycooling down the reaction mixture.

A condenser or distillation column can be attached to the reactionvessel so that byproduced water and alcohol can be removed from thevessel during the reaction. Furthermore, a vacuum can be applied to thereaction mixture to expulse the alcohol more rapidly and thus bring thereaction faster to completion.

It should be emphasized that in accordance with the present inventionthe transesterification reaction is carried out without the presence ofa solvent. After the reaction, the resulting product can be neutralizedif needed with a (weak) acid or any amphoteric compound, like water orsodium bicarbonate.

The salt of fatty acid ester of hydroxycarboxylic acid obtainedaccording to the present invention may be optionally purified bywashing, recrystallization, extraction with solution or the like toobtain a product having a higher purity.

The present invention will be elucidated with the following examples,without being limited thereto or thereby.

EXAMPLES Example 1

Methyl Laurate, Sodium Lactate and Catalyst are used in a molar ratio ofML:SL:C=1.0:1.2:0.1.

In a pre-dried distillation set-up with a nitrogen gas inlet through thereaction medium, sodium lactate (6.2 g) and catalyst (0.25 g of sodiummethoxide) are added. The reaction mixture is heated to a temperature of160° C. The sodium lactate will melt. Water or methanol will bedistilled off.

After this, the methyl laurate (10 g) is added drop wise in the courseof 10 minutes. Initially, a 2 phase system is there, but quickly, a onephase, milky type of reaction mixture is formed. The reaction iscontinued and MeOH is distilled off continuously. The temperature isincreased gradually to 200° C. and vacuum is applied and graduallybrought down to 50 mbar to keep alcohol distillation constant. Thereaction mixture is cooled down when the reaction is completed. Anoff-white to light brown, highly viscous paste is obtained. GC (rel.Area): methyl laurate 19.0; sodium lactylate 425.0.

Example 2

Methyl Laurate, Lactide and sodium hydroxide are used in a molar ratioof ML:Lact:NaOH=1.0:1.2:2.64 .

NaOH (2.46 g) was weighed out in a flask under a continuous nitrogenflow. Lactide (4.0 g) was added, along with a few drops of water. Aftera violent reaction, the temperature was put to 130° C. After a fewhours, the solution turned into a yellow paste. It was cooled to 90° C.and methyl laurate was added dropwise. The temperature was set at 150°C. and the reaction was stirred overnight. A light yellow, highlyviscous paste was obtained. GC (rel. Area): methyl laurate 86.5; sodiumlactylate 464.4.

Example 3

Methyl Caprate, Sodium Lactate and Catalyst were used in a molar ratioof MC:SL:C=1.0:1.2:0.05. In a pre-dried distillation set-up withmechanical stirrer, sodium lactate (54 g) and methyl caprate (75 g) wereadded. The reaction mixture was heated to a temperature of 160° C. Thesodium lactate melted and a two-phase liquid-liquid system was observed.The catalyst (1.3 g of sodium methoxide) was added.

Quickly, a one phase, milky type of reaction mixture was formed. Thereaction was continued and MeOH was distilled off continuously. Thetemperature was increased gradually to 190° C. Vacuum was applied andgradually brought down from 800 to 100 mbar to keep alcohol distillationconstant, during a course of 8 hours. The reaction mixture was cooleddown when the reaction was completed. An off-white to brown, highlyviscous paste is obtained. GC revealed C10 1-lactylate formation.

Example 4

Methyl Stearate, Sodium Lactate and Catalyst are used in a molar ratioof ML:SL:C=1.0:1.2:0.1. In a pre-dried distillation set-up withmechanical stirrer, sodium lactate (45 g), methyl stearate (100 g) andsodium methoxide (1.8 g) were added. The reaction mixture was heated toa temperature of 200° C. and the vacuum was set to 50 mbar. The sodiumlactate melted and a two-phase liquid-liquid system was observed.Quickly, a one phase, milky type of reaction mixture was formed. Thereaction was continued and MeOH was distilled off continuously during acourse of 8 hours. The reaction mixture was cooled down and an off-whiteto brown, highly viscous paste was obtained. GC revealed C18 1-lactylateformation.

1. A process for the preparation of a salt of a fatty acid ester ofhydroxycarboxylic acid which comprises heating a salt ofhydroxycarboxylic acid with a catalyst in admixture with a C8-C24 fattyacid ester of a lower alcohol having 1-4 carbon atoms at a temperatureat which there exists a liquid phase and subjecting the mixture to esterinterchange whereby the temperature of the process is kept at or belowthe boiling point of the C8-C24 fatty acid ester of a lower alcoholhaving 1-4 carbon atoms.
 2. The process according to claim 1 wherein theheating of a salt of hydroxycarboxylic acid with a catalyst in admixturewith a C8-C24 fatty acid ester of a lower alcohol having 1-4 carbonatoms occurs in the absence of an organic solvent.
 3. The process ofclaim 1 wherein the temperature is kept between the melting temperatureof the salt of hydroxycarboxylic acid and the boiling point of theC8-C24 fatty acid ester of a lower alcohol having 1-4 carbon.
 4. Theprocess of claim 1 wherein said hydroxycarboxylic acid is lactic acid.5. The process according to claim 1 wherein said C8-C24 fatty acid esterof a lower alcohol having 1-4 carbon atoms is a C8-C18 fatty acid esterof a lower alcohol having 1-4 carbon atoms.
 6. The process of claim 1wherein the lower alcohol of said fatty acid ester has 1-2 carbon atoms.7. The process of claim 6 wherein the fatty acid ester of a loweralcohol having 1-4 carbon atoms is methyl laurate.
 8. The process ofclaim 1 wherein said catalyst is alkaline-OR wherein R is H or Me. 9.The process of claim 4 wherein said salt of hydroxycarboxylic acid issodium lactate.
 10. The process of claim 1 wherein the molar ratio ofsalt hydroxycarboxylic acid to the fatty acid ester of a lower alcoholhaving 1-4 carbon atoms is from 0.2 to 20 mols per mol.
 11. The processof claim 1 wherein the reaction temperature is between 160-200° C. 12.The process according to claim 1 wherein water and the lower alcohol areevaporated.